This invention is related to the preparation of a novel scale inhibiting random copolymer useful in the treatment of predominantly aqueous streams such as water in recirculating cooling water systems, and milk for human consumption. More particularly, it is directed to a method for making a copolymer of (i) acrylic acid or methacrylic acid, hereafter referred to as "(meth)acrylic" acid to denote either acid, (ii) (meth)acrylamide, and (iii) certain (meth)acrylate esters of alkoxylated lower primary alcohols which alkoxylated alcohols are derived by reaction of the alcohol with a lower alkylene oxide under controlled conditions. The copolymer is substantially the only constituent of an essentially non-crosslinked random copolymer which inhibits the formation and deposition of scale-forming inorganic salts such as calcium phosphate from cow's milk during the pasteurization thereof, calcium phosphate, calcium carbonate and calcium sulfate in open-loop "process water" including cooling water systems, and boiler feed water systems. Such systems are prone to scale-forming precipitation of calcium, magnesium and iron salts, particularly calcium and magnesium phosphates, under presently preferred neutral to alkaline conditions for operating process water systems in industrial applications.
Much interest has been generated by the teachings of U.S. Pat. Nos. 3,663,448; 4,029,577; 4,324,664; 4,324,684; and 4,326,980 directed to the efficacy of various (meth)acrylic copolymers in water treatment, the relevant disclosures of which are incorporated by reference thereto as if fully set forth herein. For example, the '577 patent to Godlewski et al discloses that a copolymer of (meth)acrylic acid ("(M)AA" for brevity) or salt thereof, and, a hydroxylated lower alkyl acrylate ("HAA") is highly effective in controlling the formation and deposition of scale and/or suspended solid matter which would otherwise occur in aqueous media containing scale-imparting ions and dispersed particles. The ratio of (M)AA:HAA may be as high as 34:1 and as low as 1:4.
In U.S. Pat. No. 3,663,448 (Ralston), the formation of solid scale-forming salts in aqueous solution is inhibited by adding to the solution small amounts of certain amino phosphonate compounds, together with a water soluble polymer having a molecular weight from about 500 to about 12,000 selected from the group consisting of polyacrylic acid, copolymers of acrylic acid and up to 50% acrylamide and polyacrylamide in which at least 50% of the amide groups are hydrolyzed.
U.S. Pat. No. 4,209,398 (Ii et al) discloses yet another water treating process wherein a polymer having a structural unit derived from a monomer having an ethylenically unsaturated bond and having one or more COOH radicals, is combined with inorganic phosphates, phosphoinc acids, organic phosphonic acid esters, or polyvalent metal salts, to prevent scale formation and corrosion.
The '664 patent to Snyder teaches that the effectiveness of the '577 water-treating composition is enhanced by the addition of a water soluble ester of an aliphatic sulphodicarboxylic acid. The '684 patent to Geiger et al teaches that a compolymer of the '577 patent may be combined with a water-soluble zinc compound and a water-soluble chromate compound to enhance the corrosion-inhibiting effectiveness of the combination. The '980 patent to Snyder discloses a composition comprising an acrylic acid/lower alkyl hydroxylated acrylate copolymer which is administered to a water system in combination with an alkyl phenoxy polyethoxyethanol compound.
As is well known, in addition to the foregoing references, numerous water-soluble polymers including moieties derived from (meth)acrylamide and (meth)acrylic acid have been used to condition water containing scale-forming compounds, among which references are U.S. Pat. Nos. 2,783,200; 2,980,610; 3,285,886; 3,463,730; 3,514,476; 3,518,204; and 3,928,196. None recognized the possibility that (meth)acrylic acid and (meth)acrylamide may each have a well-defined function when they are combined to form a copolymer with an alkoxyalkyl(meth)acrylate ester ("AAE") which, by itself, is essentially insoluble in water; nor, that a copolymer of the three components may be produced in water as the solvent medium for the reaction, so as to save the expense of carrying out the reaction in a non-aqueous medium, then recovering the copolymer and reconstituting it in a desirable aqueous form for shipping.
Particularly with respect to the inhibition of Ca.sub.3 (PO.sub.4).sub.2 deposits, one might be led to believe from the prior art that poly[(meth)acrylic acid], for brevity, poly[(M)AA], and poly(acrylamide), for brevity, poly[(M)Am], might have significant activity, but a copolymer of (MA)AA and (MA)Am has very little activity. Also, a copolymer of (M)AA and an AAE, or a copolymer of (M)Am and an AAE has very little activity, and an AAE, but itself being essentially insoluble is an unlikely prospect; yet, a random essentially non-crosslinked copolymer of (M)AA, (M)Am and the AAE has been found to have excellent activity.
Further, in the foregoing closely related prior art, it was uniformly expected that (meth)acrylic acid and (meth)acrylamide were interchangeable, and that whether one or both were present, had an insubstantial effect on the scale-inhibiting activity (hereafter "activity") of any copolymer in which they were essential moieties. We have found this is not true.
As will presently be evident, (meth)acrylic acid and (meth)acrylamide are not interchangeably usable. They are both essential moieties in our copolymer, and the effectiveness of our copolymer, in addition, is critically dependent on the presence of an alkoxylated primary alcohol (APA) ester.
The terpolymer of this invention is particularly useful in cooling water systems including cooling towers, such as referred to in the foregoing prior art patents, in which systems the term "scale" applies to deposits which result from crystallization or precipitation of salts from solution. Scale formation is influenced by the temperature of the water in a particular location, the concentration of the inorganic salts dissolved in that water, the pH of the water, and other factors. It is this scale formation and deposition which is sought to be inhibited.
The current preference for treating cooling water is with a high pH and/or non-chromate corrosion inhibition program which includes phosphates and other salts which lead to the formation of calcium phosphate and other calcium salt deposits. This is equally true of boiler water systems as detailed in the Betz Handbook of Industrial Water Conditioning, 8th Edition, 1980, published by Betz Laboratories, Inc.